Power management method and system

ABSTRACT

The present invention provides a new application for an inductive coupler ( 12 ) used proximate a power transmission line ( 14 ). The magnetic field based power measurement method and system discussed herein in unique and differs from the prior technology by using near-real time intervals and periods that occur systemically in parallel with electrical systems rather than an accumulated period with little or no active capacity or proactive features. The inductive coupler ( 12 ) described herewith is used to collect, measure, and/or extract electromagnetic changes.

TECHNICAL FIELD

[0001] The invention relates to management and distribution ofelectrical power, and in particular systems for monitoring the state ofelectrical power lines and distribution grids on a real time or nearreal time basis.

BACKGROUND OF THE INVENTION

[0002] Utility companies, power distribution companies and similarentities in the United States are currently handicapped by an inabilityto accurately monitor in real time the state of power lines anddistribution grids. Thus, problems and inefficiencies often goundetected, resulting in needless expenditures and waste. The presentinvention is designed to address and rectify this situation.

[0003] Electrical power in the United States is largely transmitted inthe form of alternating current at a predetermined frequency mostfrequently 60 Hz. As is known, when current passes through atransmission line, it generates an electro magnetic field that varies infrequency and intensity with the current flowing through the line. Thesefluctuations plotted against time, are in the form of a sinusoidal wave.As is also known, reflected waves traveling in the opposite direction ofthe current flow include harmonics, transients and variations thatreflect conditions down the transmission line. Such harmonics,transients and variations in current and voltage as a function of timecan be observed, characterized and analyzed using known mathematicaltechniques. See Arrillaga, Power System Harmonic Analysis (John Wiley &Sons, 1996), chapters 4, 6, 7 and 9. Events occurring to thetransmission line such as shorts, lightning strikes, changes in load andsimilar conditions also generate transient variations that are reflectedin the electro magnetic field surrounding the transmission line. Themagnitude and frequency of such harmonics, transients and variations canbe measured and in accordance with the invention, the data collected andprocessed to reflect events and occurrences affecting the transmissiongrid. Thus, in accordance with the invention, monitoring and measuringchanges in the electro magnetic field surrounding the transmission line,enables real time or near real time monitoring of the state of thetransmission line. The state of the line may be charged with high or lowvoltage, or be without current or charge. As used herein the terms “realtime” and “near real time” refers to time required for a computer toreceive and process one or more input data streams and output a signalor value based upon the input data. Thus, in most instances, “real time”will be measured in seconds or fractions of a second.

[0004] Stewart U.S. Pat. No. 5,982,276, the disclosure of which ishereby incorporated by reference, describes a system for communicatinginformation between subscribers over power transmission lines whichnormally convey electrical power to a plurality of diverse electricalsites for providing electrical power to electrical devices disposed atthese diverse electrical sites. This communication system makes use ofan inductive coupling to receive the transmitted information from themagnetic field surrounding the power transmission line. The inductivecoupler is preferably a ferroceramic type of inductive coupler having asensitivity such as 10⁻²³ volts. The present invention utilizesinductive couplers to detect changes in the electromagnetic fieldsurrounding a transmission line, measures the changes and utilizes thedata to identify conditions and events occurring on the transmissionline.

SUMMARY OF THE INVENTION

[0005] The present invention provides a new application for an inductivecoupler used proximate a power transmission line. The magnetic fieldbased power measurement method and system discussed herein in unique anddiffers from the prior technology by using near-real time intervals andperiods that occur systemically in parallel with electrical systemsrather than an accumulated period with little or no active capacity orproactive features. The inductive coupler described herewith is used tocollect, measure, and/or extract electromagnetic changes.

[0006] The present invention provides a system and method for gatheringdata from one or more inductive couplers. The collected data reflectspower surges, demand shifts, and system breakdowns on a real time ornear real time basis. Data collection may be timed by reference to anatomic clock signal in order to obtain accurate results from a pluralityof locations at once. The system provides the capability of using thecollected data in conjunction with stored data, such as historical data,local and nation power grid layout data, topographical information anddynamic information such as weather data to identify, characterize andlocate power transmission problems and conditions that need attention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In the accompanying description:

[0008]FIG. 1 is a schematic representation of a power management systemaccording to the invention;

[0009]FIG. 2 is a flow chart illustrating steps utilized in the practiceof the invention;

[0010]FIG. 3 is a graphical representation of an event detected by thesystem of FIG. 1;

[0011]FIG. 4 is a schematic representation of an inductive coupleraccording to the invention.

[0012]FIG. 5 is a schematic representation of a power transmission gridemploying a plurality of magnetic couplers to provide real timeinformation reflecting the condition of the grid.

DETAILED DESCRIPTION

[0013] According to one embodiment of the invention as shown in FIGS. 1and 2, a power management system 10 according to the invention includesone or more sensors (inductive couplers) 12 disposed in proximity to oneor more power transmission lines 14. In practice, coupler 12 is clampedonto the power line at a convenient location in order to detectfluctuations in the voltage and current flowing through transmissionline 14. As set forth in detail below, inductive coupler 12 includes anantenna and coils each of which are connected via a microwave cable 11to a microwave converter 16 such as a HP model 8902 B analyzer, whichfilters the signals. Microwave cable 11 is configured similarly to astandard coaxial cable with a center conductor and an annular conductiveshield, except that the shield of microwave cable 11 is typically a foilor layer of conductive material as opposed to the mesh used in typicalcoaxial cable. In the system illustrated in FIGS. 1 and 2, the centerconductor of microwave cable is utilized as a first channel conductorand the shield is used as a second channel conductor.

[0014] As illustrated, a first two channel clock signal generator 18 anda second four channel clock signal generator 20 provide a clock signalon four channels, two of which are used for system calibration with thesecond two dedicated to sampling frequency. Currently availabletechnology is limited to a clock frequency of approximately 300 Ghz,however, as faster clocks become available, it is anticipated that suchfaster signal generators may be utilized in the practice of theinvention. The clock signals are input to a digital generator oroscilloscope 24 such as ESG signal generator model E4422B which in turngenerates a reference waveform signal to converter 16 and spectrumanalyzer 26. In one variation, spectrum analyzer 26 is a Hewlett PackardSeries 89400 vector signal analyzer. Spectrum analyzer 26 utilizes theclock signal to convert the analog signals from microwave converter 16into digital form. The digital data or Bitstream from analyzer 26,representing changes in the magnetic and electric fields surroundingpower line 14, is input to a processing system 30 including one or morecomputers 32 and communications interfaces 36 a, 36 b, 36 c (FIG. 2).Computer 32 may be local or remote relative to the other components. Ifcomputer 32 is at a distant location, then suitable means such as anetwork are provided for transmitting the output of analyzer 26 tocomputer 32.

[0015] In order to prevent spurious inference from signals in the powersupply from interfering with the operation of the system components,converter 16, clock signal generators, 18 and 20, oscilloscope 24,analyzer 26 and computer 32, along with any associated auxiliarycomponents, are enclosed within a Faraday cage 22. Additionally, thepower source for these components is supplied from a source such as theprimary side of the step down transformer supplying transmission line14, the source being filtered to further isolate the components fromtransmission line 14.

[0016] As schematically represented in FIG. 2, system 30 includes ahistorical database 40 reflecting prior states of the transmission line14 including a “normal state,” data associated with prior events suchas, lightning strikes, line failures or shorts and other abnormalconditions, along with the classification of such events. Database 40 isconstructed using frequency and power measurements from inductivecoupler 12 and associating the occurrence of known events such aslightning strikes, grounds, equipment failures and similar conditionswith transients measured at the time of the event. For example, if atransformer shorts out, inductive coupler 12 will detect a transientresulting from the short and the data associated with the transient willbe recorded in data base 40. When the cause of the transient isidentified, it is logged into the database by an operator. Subsequently,when computer 32 observes a transient having the same or similarcharacteristics, it will identify the source of the transient as atransformer failure based upon the data recorded in historical database40.

[0017] An hypothetical example of an event is graphically represented inFIG. 3 wherein solid line represents historical data corresponding tothe amplitude of a selected parameter, for example reflected voltage ata given frequency over a period p. A change in the amplitude of theamplitude of the parameter at a point during the period, represented bythe dotted line at A, indicates an event or changed condition affectingthe transmission of power over line 14. When computer 32 registers thechange, the computer will search database 40 for a similar occurrenceassociated with a known event or condition and activate an alarm toalert the operator. It will be appreciated that the hypothetical examplerepresented in FIG. 3 is only for the purpose of illustration; theactual parameters used to characterize the state of the transmissionline may vary from case-to-case depending upon the particular system andwill include values that are represented by complex numbers such asimpedance or admittance (phasors), or multidimensional quantities(tensors) that include a component for each of a plurality ofdimensions. See Arrillaga, Power System Harmonic Analysis (John Wiley &Sons, 1996)(chapter 10, describing iterative harmonic analysis).Analysis of the electro magnetic field surrounding a three-phasetransmission line, in which the phases are 120⁰ apart, becomes even morecomplex.

[0018] System 30 also includes a grid map of the local distributionsystem along with a national grid map maintained on one or moredatabases 42, along with National Means Data relating to the nationaltransmission and distribution system that is maintained in a database44. Geo-Spacial data such as the topography of the local distributionarea is maintained on yet another database 46 which is linked via agraphic to a dynamic data collection, retrieval and display platform 47such as Boeing Autometric's EDGE® system which includes tools forintegrating imagery, maps, terrain, models and weather data.

[0019] Preferably, databases 40-46 are maintained on local storage mediasuch an internal hard disk in computer 32, however, the data bases maybe maintained on remote devices, accessed by computer 32 via a wirelessor hardwired connection such as a telephone modem or network. In somecases, it may be desirable to distribute the computing function,depending upon the amount of data collected, the size of databases 40-46and the desired output, in which case additional computers locatedeither locally or remotely may be employed in addition to computer 32.

[0020] In operation, computer 32 receives collected and processed datafrom analyzer 26 and incrementally compares the data to historical datafor a period corresponding to a portion of the base frequency cycle (60Hz). For example, data collected for a period of one millionth of secondbeginning at a selected location in the cycle (between 0 and 360degrees) can be compared to the corresponding increment from thehistorical database at step 50. If an abnormal condition is detected,typically in the form of a transient or a variation from the “normal”condition of transmission line 14, computer 32 attempts to identify thesource of the abnormality by comparing the variation in the waveform toabnormalities associated with historical events stored in database 40.

[0021] For example, a lightning strike will generate a very large, veryrapid increase in voltage along with an increase in current. On theother hand, the sudden opening of a large circuit breaker may alsoresult in a voltage surge, however the duration of the surge will bedifferent and the current will drop. Computer 32 will distinguish andidentify the two different events based upon historical data associatedwith similar events that occurred in the past.

[0022] Depending upon the classification and magnitude of the event,computer 32 may also alert the system operator with an alarm. In theevent that computer 32 is unable to classify the detected abnormality,computer 32 creates a new event classification for inclusion in thedatabase. When the source or event causing the particular abnormality isidentified, the database is updated.

[0023] In addition to identifying abnormal conditions and the source ofsuch conditions, computer 32 determines the distance of the event oroccurrence from the inductive coupler through the use of knownmathematical techniques. See Chowdhure, Electromagnetic Transients inPower Systems, (1996, Research Studies Press LTD and John Wiley & Sons,Inc., Chapters 2, 8 and 10). For example, in the case of a feeder lineconnected to several step-down transformers, a lightning strike to oneof the stepped down lines will result in voltage and current transientsas described above in the feeder line. Using one or more of historicaldata from database 40, the distance from the inductive coupler and thelocal grid map from data base 42, computer 32 can determine which of thesegments was struck. Utilizing the local grid map from data base 42,computer 32 can then generate a graphical display including the grid mapshowing the location of the strike and output the map via interface 36 bto a display such as CRT monitor 54. Further, in a preferred embodiment,computer 32 accesses Geo-Spacial data base 46 to include the topographyof the area where the strike occurred into the graphical display,including access roads and similar information. If desired, computer 32can also access data platform 47 to incorporate additional real timeinformation such as weather conditions that may be the source of anabnormal condition along with other potentially useful information intothe graphical display. All of the forgoing functions are performed on areal time basis.

[0024] Turning to FIGS. 1 and 4, an inductive coupler 12 clamped onto 13KVA transmission line 14 to detect changes in the electro magnetic fieldsurrounding the line includes first and second windings or coils 62 and64 formed from a continuous piece of number 2 copper/aluminum alloy wireconnected at a first end 63 to the center conductor of microwave cable11 and terminating at an unconnected second end. Windings 62 and 64 arespaced approximately 10 cm apart and each include five turns 61 with adiameter of approximately 3 cm that are offset from a line perpendicularto a longitudinal axis of coupler 12 at an angle α. Since coupler 12 ismounted with its longitudinal axis substantially parallel totransmission line 14, windings 62 are 64 are also offset from a lineperpendicular to transmission line 14. As illustrated, windings 62 and64 are configured and positioned to detect changes in the magnetic fieldsurrounding transmission line 14 reflecting changes in the currentflowing through the transmission line. The spacing of the coils relativeto each other results in simultaneous measurements corresponding to twopoints on a waveform propagated along transmission line 14.

[0025] Since windings 62 and 64 are angled relative to a lineperpendicular to transmission line 14, the current induced in windings62 and 64 will be phase shifted relative to the current flowing throughtransmission line 14. Angle α may be varied within a range greater than0 up to the limits imposed by the geometry of the other components ofcoupler 12; however, in a preferred embodiment, a is in the range offrom 10 to 14 degrees and most preferably about 12 degrees (between 11and 13 degrees).

[0026] Disposed within windings 62 and 64 is a millimeter band radiowave antenna 66 comprising a set of parallel grading windings 65 formedfrom a continuous length of number 2 copper/aluminum alloy having afirst end 67 connected to the shield of microwave cable 11 andterminating at a second unconnected end. As illustrated, gradingwindings 65 of antenna 66 are positioned parallel to transmission line14. Antenna 66 is configured by fractional wavelengths of harmonicsbased upon a 60-Hz transmission frequency with the length of the longestgrading winding 65 being approximately 7.5 inches and the length of eachof the shorter windings determined by parametric estimation of thedifferences between the wavelength of the harmonics. Antenna 66 iscapable of detecting signals having a frequency of up to approximately300 Ghz. As will be appreciated, antenna 66 is designed and positionedto detect the frequency and magnitude of voltage changes in transmissionline 14. Further, since windings 62 and 64 are angled relative toantenna 66, the signal from windings 62 and 64 will also bephase-shifted relatively to the signal from antenna 66. Generatingphase-shifted signals in this fashion provides for ease of computationwhen employing the above-referenced mathematical techniques used toprocess the signals from the windings and the antenna.

[0027] Windings 62 and 64 along with antenna 66 are enclosed in anon-conductive body or housing 70 such as a length of PVC pipe. In apreferred embodiment, the interior surface of housing 70 is coated witha conductive paint 72 in order to protect coupler 12 from lightningstrikes. During the assembly of coupler 12, housing 70 is filledpolycarbonate filler material 74 that serves to maintain windings 62 and64 and 66 in position within the housing and isolate the windings andantenna from each other and from conductive coating 72. Housing 70 isalso provided with end caps 76, (one shown) that are glued or otherwisesecured onto housing 70. First end 63 of the wire forming windings 62and 64 and first end 67 of the wire forming antenna 66 extend through ahole (not shown) in one of end caps 76 and are connected to microwavecable 11 in the manner described above.

[0028] As will be appreciated, currents and voltage fluctuations intransmission line 14 will induce corresponding currents and voltages incoils 62, 64 and antenna 66. Power management system 10 measures themagnitude, frequency and duration of these currents and voltages toidentify conditions and events occurring on transmission line 14.Further, power management system 10, utilizing the appropriatemathematical techniques, can determine values for time and frequencydependent parameters such as impedance and reactance, as well asidentifying changes in inductance and capacitance by analyzing changesor shifts in phase of voltage and current. Additionally, even morecomplex parameters, represented as tensors, may be determined using thedata obtained via magnetic coupler 12. Each of such parameters providesa means of characterizing or modeling the condition of transmission line14 on a real time basis that individually or when combined with otherparameters, provides a means of identifying and characterizing eventsand conditions on transmission line 14 that has not been previously beenavailable.

[0029] Referring now to FIG. 5, a problem encountered in “wheeling”power between power grids is the lack of sufficient real timeinformation needed to efficiently distribute and allocate availablepower over a distribution system. As described below, in one embodiment,the invention addresses this problem by supplying real time informationthat enables power distribution and redistribution between power gridson a real time basis. FIG. 5 illustrates a system according to theinvention for monitoring a number of power transmission lines formingall or part of power distribution system or grid 80 includes a pluralityof inductive couplers 82 positioned proximate power transmission lines84 at different locations within for detecting voltage and currentfluctuations in the power transmission lines. Each of couplers 82 isconnected to a transmitter 86 that transmits a signal corresponding tothe current and voltage fluctuations detected with the coupler to areceiving and processing station 90. Transmitters 86 may be wirelessunits such as a radio frequency transmitter or a hardwired unit such asa telephone modem and may be provided with any required signalprocessing equipment such as clocks, filters, converters andoscilloscopes as needed to process the collected data into atransmittable signal. The signal from each transmitter 86 is received ata central processing station 90, decoded, processed and integrated withthe signals from other transmitters 86 to provide real time or near realtime data reflecting the condition of the distribution system 80. Theavailability of this information on a real time basis enables efficientdistribution and allocation of power over distribution system 80.

[0030] While certain embodiments of the invention have been illustratedfor the purposes of this disclosure, numerous changes in the method andapparatus of the invention presented herein may be made by those skilledin the art, such changes being embodied within the scope and spirit ofthe present invention as defined in the appended claims.

1. A power management system comprising: a sensor positioned adjacent anelectrical transmission line carrying alternating current, the sensorcomprising at least two measurement elements configured to generate asignal proportional to the magnitude of changes in the electro magneticfield surrounding the transmission line; and a system for processing thesignals generated by the elements, the system processing the signals andgenerating an output that indicates changes in the condition of thepower transmission line on a real time basis.
 2. The power managementsystem of claim 1 wherein the system for processing the signals includea computer and a database including historical data for the transmissionline.
 3. The power management system of claim 2 further comprising adata base including one or more grid maps, the computer using the gridmap to generate a graphical representation of a power distributionsystem connected to the transmission line including the location of thesource of the change in condition of the transmission line.
 4. The powermanagement system of claim 3 further comprising a database includingtopographical information for the geographic area served by the powerdistribution system, the computer using the topographical information togenerate a graphical representation of the power distribution systemincluding the topology of the geographical area covered by the powerdistribution system.
 5. The power management system of claim 1 whereinsensor generates a signal proportional to a transient voltage on thepower transmission line.
 6. The power management system of claim 1wherein the sensor generates a signal proportional to a harmonic voltageon the power line.
 7. The power management system of claim 1 where thefirst measurement element is configured to generate an output that isphase shifted relative to the output of the second measurement element.8. The power management system of claim 2 wherein the historicaldatabase includes data representing a previously measured transient onthe power transmission line and the identify of the source of thetransient.
 9. A sensor configured to be positioned adjacent and parallelto an electrical transmission line carrying alternating current,comprising: a casing; a first electrical conductor disposed inside thecasing having at least one turn therein to provide a pair of parallellinear segments of unequal length each extending in a lengthwisedirection of the sensor; a second electrical conductor in the form of acoil disposed around the first conductor; a first lead connected to thefirst conductor for conducting a signal from the first conductor throughthe casing to an external signal analyzer; and a second lead connectedto the second conductor for conducting a signal from the secondconductor through the casing to an external signal analyzer.
 10. Thesensor of claim 9, wherein the first conductor comprises a pair ofparallel coils spaced apart in the lengthwise direction of the sensorand a segment connecting the coils.
 11. The sensor of claim 10, whereinaxes of the pair of parallel coils are set at an angle in the range of10 to 14 degrees relative to the lengthwise direction of the sensor. 12.The sensor of claim 10, wherein the first conductor has at least sixturns at one end thereof providing at least seven parallel segments ofdifferent lengths effective for monitoring a range of emissions from thetransmission line.
 13. The sensor of claim 12, wherein the casecomprises a solid cylinder made of electrically insulating plastic inwhich the first and second conductors are embedded.